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Discussion Starter · #1 ·
hey guys,

i have an 88 626 turbo, with an ATX to MTX swap.

im having a severe problem with mileage.

before you go saying things about search and do a tune up, know this

new:

wires
plugs
distributor cap
rotor
o2 sensor
thermo sensor (the one for the computer)
compression test 135 across all cylinders

tested:
o2 sensor
thermo sensor
spark (good hot blue)


the vehicle is getting roughly 15mpg when i used to get almost 32.

it has a rebuilt head, new gas tank, no gas leaks. The egr system is working and was recently redone.

any input or ideas are greatly welcomed.

thanx guys

if i missed any info, just let me know.. ill post anything else needed
 

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fuel filter maybe?

Did you run the codes?
 
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Discussion Starter · #3 ·
new fuel filter 8 months ago, unlikely thats it, although ill check

no codes whatsoever

this problem is really starting to annoyme

(oh, and i tried a different ECU, had one lyin around, no avail)
 

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Is the cat okay? Sometimes trashing a head and all that crap going through the exhaust can really mess up a cat.
Have your driving habits changed? Using different gas? Is it lacking power or running bad in any way?
 

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did this ever get solved because im having a similar problem and I have replaced everything I can think of except for fuel filter and getting a tuneup, I dont know when the last time this car had a tune up was, but ive had it for almost a year and never gotten one.
 
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Discussion Starter · #6 ·
odd that you should ask that


was talkin to a mechanic of like 25 years, he suggested the fact that i didnt have the cat on as the problem,

fine, i got my old one, we looked at it,... blew out the carbon, put it on

****in thing made the mileage just a little worse,... not much mind you,.. but a little

same fuel, regular unleaded, same driving habits,

and as for the driving habits thing, its kinda funny, the friggin thing gets the same mileage whether i drive it like a granny or like i stole it

also, when i pull the plugs, they are black, really black, not with build up, but more like jsut a black coating, smells like gas (go figure)
 

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15 mpg

northernmaniac said:
this problem is really starting to annoyme
(oh, and i tried a different ECU, had one lyin around, no avail)

Hey Northernmaniac;
My gut feeling is that even though you tried another ECU, is that may be a place to focus your attention. The ATX and MTX undoubtebly have different parameters. Was the original wiring harness and ECU re-used ?
The controls for the air/fuel ratio may be mixed up and in a failsafe mode. Maybe the computer thinks the car is cold.
 

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You must also make sure that the ECU is off of the same year engine. I think theres a major difference in fuel managment from the 88-89 and the 90-92
 

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Ok so ive thought about this and from what I know about my car and what ive read on here , this is my hypothesis.

My car gets crappy mileage since the day I got it, its had new plugs, wires, cap, and rotor, better air filter, and new o2 sensor. Yet the mileage is still crappy.

A few months ago I had to replace the fuel pressure regulator. THe regular pressure gauge wouldnt hook up to the car so my mechanic used a different one that would but that he knew was incorrect in its readings. HOwever the psi to the injectors at first was 85 psi (book value is close to 35psi I belive), after replacing the fuel pressure regulator we got it down to about 65psi.

THen I asked on this website why this would happen, I was told that if there is a vacuum leak the FPR will up the psi. THen a few weeks later I got code 17 running rich from the O2 sensor the book says that vaccum leak is also a cause for a code 17, I just replaced the o2 sensor instead.

Still getting crappy mileage, I have a feeling that it is caused by a vaccum leak, Im going to check my tb boot and then go from there. Also I noticed that the part of the pcv system that connects closest to the vaf is loose. WOuld this make a difference in vaccum?
 

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vacuum

TiZBaD99 said:
Ok so
THen I asked on this website why this would happen, I was told that if there is a vacuum leak the FPR will up the psi. THen a few weeks later I got code 17 running rich from the O2 sensor the book says that vaccum leak is also a cause for a code 17, I just replaced the o2 sensor instead.

Still getting crappy mileage, I have a feeling that it is caused by a vaccum leak. Also I noticed that the part of the pcv system that connects closest to the vaf is loose. WOuld this make a difference in vaccum?

Hey TiZBaD;
Anything loose dealing with the vacuum system is not good. Also check your EGR's vacuum lines and solenoid on the firewall. These lines and solenoids can become plugged inside, which in return can restrict vacuum flow. An easy test is to blow through the lines.
 
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Discussion Starter · #11 ·
ecu is the same... i dont think the problem is electrical, have tested most things and they are all fine,

also, ecu is not throwing codes at all

the engine behaves just like its running rich

next step is test the fuel pressure

i will keep you all updated!
 

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tizbad yes having a vacuum leak there will kill your mileage.

Northernmaniac check out the rubber/plastic pipe going from your airflow meter to the throttle body for cracks.
 
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Discussion Starter · #13 ·
no cracks.. all intake rubbers in great shape

the hose that plugs into the airbox, where does it go to?

u know the one that always breaks off
 

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hose to airbox

If you are referring to the one that comes off the bottom of the TB intake, that's a resonance chamber used for accumulating air from the intake boot.
 
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Discussion Starter · #15 ·
nope... on the stock airbox, there is a what looks like a vacuum hose that hooks onto a nipple on the airbox that always breaks off. nowhere near the tb boot, and the resonance chamber on the gt's exists in the fender, not after the VAF
 
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